Internet DRAFT - draft-gershenfeld-thtp
draft-gershenfeld-thtp
Network Working Group N. Gershenfeld
Internet-Draft CBA/MIT
Intended status: Informational D. Johnson
Expires: April 4, 2007 Sun Microsystems, Inc.
T. Snide
Schneider Electric
K. Lynn
Cisco
October 2006
Trivial Hypertext Transfer Protocol (THTP)
draft-gershenfeld-thtp-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 4, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Gershenfeld, et al. Expires April 4, 2007 [Page 1]
Internet-Draft THTP October 2006
Abstract
THTP, the Trivial Hypertext Transfer Protocol, is an implementation
of HTTP over UDP transport. THTP is designed for environments with
limited computational power or bandwidth and single-packet exchanges.
As such, THTP is best suited for the emerging class of applications
running on embedded devices and sensor networks. THTP decouples HTTP
from TCP and provides a subset of HTTP's functionality, in particular
leveraging HTTP's URI naming scheme. This document describes the
THTP protocol.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. THTP Design . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Protocol Relationships . . . . . . . . . . . . . . . . . . 4
2.2. URI Format . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Request Model . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Reliability . . . . . . . . . . . . . . . . . . . . . . . 5
2.5. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 5
3. HTTP Features . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. GET Method . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. POST Method . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Status Code Definitions . . . . . . . . . . . . . . . . . 8
3.3.1. Successful 2xx . . . . . . . . . . . . . . . . . . . . 8
3.3.2. Client Error 4xx . . . . . . . . . . . . . . . . . . . 8
3.3.3. Server Error 5xx . . . . . . . . . . . . . . . . . . . 8
3.4. Proxies . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.5. Caching . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
Gershenfeld, et al. Expires April 4, 2007 [Page 2]
Internet-Draft THTP October 2006
1. Introduction
The HTTP protocol [RFC1945] introduced a powerful naming construct
that simultaneously identifies and locates resources. The
anticipated proliferation of smart, tiny, networked devices require a
standards-based naming scheme [ieee-i0], [i0], but often cannot
tolerate the overhead necessitated by the current tight coupling
between HTTP and TCP [RFC0793]. Specifically, small, inexpensive
embedded devices and sensors receiving or sending single-packet
commands and responses require neither mandated reliable network
transport nor packet sequencing at the transport layer.
For example, the application of a networked light switch sending an
"on" instruction to a networked light bulb in the same physical room
does not need the overhead of a TCP full three-way handshake. In
addition, implementing TCP or even T/TCP [RFC1644] is prohibitively
expensive in terms of the communication and state machine complexity
on such a resource constrained computing platform.
This document details Trivial Hypertext Transfer Protocol or THTP, an
application-layer protocol. THTP is a scaled-down adaptation of HTTP
designed to run over the UDP [RFC0768] transport layer. It is not
intended as a replacement of HTTP over TCP, but rather a
complementary scheme to widen the range of possible environments
where HTTP-like semantics are used. For example, a similar but more
complex scheme is used by UPnP [upnp]; THTP codifies a simple,
portable, standards-based means of extending HTTP to UDP.
Gershenfeld, et al. Expires April 4, 2007 [Page 3]
Internet-Draft THTP October 2006
2. THTP Design
THTP is designed to be lightweight and easy for applications and
application designers to implement. THTP uses HTTP's URI naming
scheme. THTP differs from HTTP in several important ways. These
differences are conscious design decisions based on THTP's intended
environment of limited computational power or bandwidth and single-
packet exchanges. This section details critical aspects of the THTP
design.
2.1. Protocol Relationships
THTP uses UDP [RFC0768] as its transport layer. Figure 1 shows the
relationship between THTP and various Internet protocols.
Protocol Relationships
+-----+ +------+ +------+ +------+ +-----+
| FTP | | HTTP | | TFTP | | THTP | ... | ... |
+-----+ +------+ +------+ +------+ +-----+
| | | | |
+-------+ +---------+ +-----+
| TCP | | UDP | ...... | ... |
+-------+ +---------+ +-----+
| | |
+------------------------------------------+
| IP (Internet Protocol) |
+------------------------------------------+
| |
+------------------------+ +------------------------+
| Local Network Protocol | | Local Network Protocol |
+------------------------+ +------------------------+
Figure 1
2.2. URI Format
THTP defines a naming scheme analogous to HTTP's Uniform Resource
Locator (URL) which has been subsumed into the more abstract notion
of a Uniform Resource Identifier (URI) [RFC3986]. THTP leverages the
URI naming and large base of existing implementations to provide an
efficient means of addressing and communicating with devices in a
range of environments.
A THTP URI is semantically identically to those in HTTP, but with UDP
as transport. The THTP URI format is defined as follows:
THTP_URI = "thtp:" "//" host [ ":" port ] [ abs_path [ "?" query]]
Gershenfeld, et al. Expires April 4, 2007 [Page 4]
Internet-Draft THTP October 2006
THTP URIs are processed identically to HTTP URIs. THTP uses UDP port
80 by default, but may use other UDP ports via the optional port
specification in the URI.
2.3. Request Model
In contrast to the request/response paradigm of HTTP, responses in
THTP are not required. Responses may be either unnecessary or
implicit via an out-of-band channel. Note that THTP does not
preclude request responses, however it explicitly separates the two
functions. A user may query the state of the light bulb remotely,
receive a notification that the filament is burned out, or require a
device to periodically report its status via THTP. The separation of
request and response in THTP has several design implications, most
notably on reliability and message size.
A THTP message must fit entirely in a single UDP packet. THTP cannot
transfer data larger than a single packet in a single request.
Applications that require ordered delivery, large messages, flow
control or congestion control should use HTTP (over TCP). Multiple
messages cannot be placed within a single THTP packet. As such,
"chunked" transfer-coding is not allowed.
2.4. Reliability
THTP uses UDP as its transport layer. Since UDP is an unreliable
transport protocol and THTP does not include reliability, THTP makes
no guarantees of packet delivery. For example, light switches and
home appliances, the user receives immediate feedback: the room
illuminates, therefore the request over the network was successful.
If the packet is lost and the light bulb does not light, the user can
actuate the light switch again.
However, THTP does not preclude reliability at other layers where
necessary to support specific applications. Consider for example an
application that requires lightweight, reliable single-message
passing but not ordered delivery. Such an application could use THTP
in conjunction with reliability at the physical or application layer.
In addition, automated systems without an out-of-band feedback
mechanism require additional verification, either by actively
querying the state of the remote device or by adding application
layer reliability.
2.5. Multicast
Because THTP uses UDP, it is possible to send a THTP message to a
multicast group address. Assuming the underlying data-link layer
network supports broadcast or multicast transmission, a single THTP
Gershenfeld, et al. Expires April 4, 2007 [Page 5]
Internet-Draft THTP October 2006
message could be sent to, and received by, multiple nodes. An
immediately practical application is to assign locally scoped
multicast group addresses to a set of nodes. For example, a single
light switch might send a THTP "on" instruction to multicast group M.
All light bulbs assigned to group M would receive the message and
switch on. While Internet multicast deployment is limited, THTP
multicast messages are useful in many local area networks.
Gershenfeld, et al. Expires April 4, 2007 [Page 6]
Internet-Draft THTP October 2006
3. HTTP Features
THTP must implement a minimum subset of HTTP's features, but is not
required to implement all of HTTP. The subset of features THTP must
support are a natural consequence of using UDP and maintaining
simplicity. Additional HTTP mechanisms may be implemented on an
application specific basis by prearrangement. However, a THTP server
may always legally respond with the status code 501 (not implemented)
as needed. Status codes are documented in Section 3.3.
At a minimum, THTP clients and servers must support the HTTP GET and
POST methods. A server must always respond to a GET request or
provide the appropriate status code error. A server may respond to a
POST request or provide the appropriate status code error. A server
must respond with an error on an error event regardless of the method
type.
3.1. GET Method
THTP and HTTP's use of the GET method are identical. THTP must
support the GET method. A THTP GET request from a client expects a
response and the server must send the requested object identified by
the Request-URI or an error. If the Request-URI refers to a data-
producing process, the data from that process is returned.
To send information from the client to the server process, a client
may imbed that information in the HTTP URI and use the GET method.
The user agent appends a '?' to the action URI along with the data
set in `application/x-www-form-urlencoded' format.
THTP may support "conditional GET" in instances where cached entities
can be used without consuming unneeded network bandwidth
3.2. POST Method
THTP must also accept the POST method, but uses POST in a slightly
different manner than HTTP. A THTP server may respond to a
successful POST, but is not required to do so. The optional response
covers cases where the client is not expecting a response and where
communication resources are scarce, for instance sensor nodes. In
the case of a lightbulb and lightswitch, a POST request may be used
to change the state of the light and does not require a response.
However, a THTP server must always respond with an error status code
on an error condition.
The POST method requests that the destination server process the data
within the request as a subordinate of the the Request-URI resource.
To perform an action with a POST, the user agent uses the action URI
Gershenfeld, et al. Expires April 4, 2007 [Page 7]
Internet-Draft THTP October 2006
and adds a message body of type `application/x-www-form-urlencoded'.
3.3. Status Code Definitions
THTP uses the same status codes as defined by HTTP. THTP servers
must implement the following status codes at a minimum:
3.3.1. Successful 2xx
200 OK The 200 successful status code differs slightly from that in
HTTP due to it being optional for POST requests. Code 200 indicates
that the request has succeeded. A successful GET request must result
in response containing the 200 status code along the information
queried. A POST request may return a 200 status code.
3.3.2. Client Error 4xx
400 Bad Request The request is malformed and rejected by the server.
404 Not Found The request cannot be honored by the server because the
requested resource is not available.
3.3.3. Server Error 5xx
501 Not Implemented The request cannot be honored by the server
because the server does not support the requested functionality.
Such an error may occur for unsupported methods.
3.4. Proxies
THTP messages may be proxied. Proxies are a natural consequence of
interconnecting a local area network, e.g. for home automation, with
the larger Internet.
3.5. Caching
HTTP explicitly allows and makes provisions for content caching. A
request may be honored by an intermediary other than the final
recipient. When cached, the response comes from this intermediary.
Clearly, in THTP's intended environments such as control and
automation networks, caching is not expected. Caching is not
explicitly forbidden, but THTP's request model anticipates all
requests to be carried through to the final recipient,
Gershenfeld, et al. Expires April 4, 2007 [Page 8]
Internet-Draft THTP October 2006
4. Security Considerations
Since THTP is implemented on top of UDP, many of the security issues
inherent in UDP are inherited by THTP. By eliminating the minimal
source validation afforded by the three-way handshake of TCP, THTP is
vulnerable to source IP address spoofing. Without a stronger means
of authentication, THTP must rely on provider ingress filtering
[RFC2827]. Instead, THTP may use appropriate lightweight encryption
[sea] and/or authentication.
Gershenfeld, et al. Expires April 4, 2007 [Page 9]
Internet-Draft THTP October 2006
5. References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC1644] Braden, B., "T/TCP -- TCP Extensions for Transactions
Functional Specification", RFC 1644, July 1994.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[i0] Gershenfeld, N., Krikorian, R., and D. Cohen, "The
Internet of Things", Scientific American , October 2004.
[ieee-i0] Gershenfeld, N. and D. Cohen, "Internet 0: Interdevice
Internetworking", IEEE Circuits and Systems ,
October 2006.
[sea] Standaert, F., Piret, G., Gershenfeld, N., and J.
Quisquater, "SEA: a Scalable Encryption Algorithm for
Small Embedded Applications", CARDIS , April 2006.
[upnp] Goland, Y. and J. Schlimmer, "Universal Plug N' Play
Forum", http://www.upnp.org/ .
Gershenfeld, et al. Expires April 4, 2007 [Page 10]
Internet-Draft THTP October 2006
Appendix A. Acknowledgments
The authors gratefully acknowledge the contributions of
(alphabetically): Robert Beverly, Danny Cohen, David Dalrymple, and
Karen Sollins.
Gershenfeld, et al. Expires April 4, 2007 [Page 11]
Internet-Draft THTP October 2006
Authors' Addresses
Neil Gershenfeld
Massachusetts Institute of Technology
Room E15-411
20 Ames Street
Cambridge, MA 02139
US
Phone: +1 617 253 0392
Email: gersh@cba.mit.edu
Douglas Johnson
Sun Microsystems, Inc.
Mailstop UBUR02-306
One Network Drive
Burlington, MA 01803
US
Phone: +1 781 442 0716
Email: douglas.johnson@sun.com
Todd Snide
Schneider Electric
1 High Street
North Andover, MA 01845
US
Phone: +1 978 975 9472
Email: todd.snide@us.schneider-electric.com
Kerry Lynn
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
US
Phone: +1 978 936 1342
Email: kelynn@cisco.com
Gershenfeld, et al. Expires April 4, 2007 [Page 12]
Internet-Draft THTP October 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Gershenfeld, et al. Expires April 4, 2007 [Page 13]
